The present invention relates to a device useful as a controllable variable speed thruster-driven oceanographic profiler for coastal waters for measuring the vertical structure of chosen properties of the oceanic water column.
The best known method of profiling the properties of the ocean water column is the CTD (Conductivity-Temperature-Depth) system used widely in most modern oceanographic vessels. In these systems, CTD and other oceanographic sensors are mounted beneath a water sampling rosette ensemble, all of which can be lowered from the hydrographic winch on the ship. As the system moves through the water column, sensor data is transmitted through the winch wire to a shipboard data logger which also controls the sequence of closures of the sampling bottles on the rosette, and the storage of data. These devices are large, cumbersome and expensive to operate at sea, and in addition face the problem of the motion of the ship being coupled into the winch wire thereby possibly affecting the measurement process.
Early oceanographic profilers were first designed to measure ocean current flows. A variety of forms have evolved over several decades starting in 1965 with the free drop technique used by Richardson et al (W. S. Richardson and W. J. Schmitz (1965), xe2x80x9cA technique for the direct measurement of transport with application to the Straits of Floridaxe2x80x9d, J. Mar. Res., Vol 23, pp 172-185), then the wire guided profilers of Duing and Johnson (W. Duing and D. Johnson (1972), xe2x80x9cHigh resolution current profiling in the Straits of Florida xe2x80x9c, Deep-Sea Res., Vol 19, pp 259-274), the bottom mounted winch-based profiler of Walden and Collins (R. G. Walden and C. W. Collins (1984), xe2x80x9cBottom-mounted profiling winch xe2x80x9cWHOI Technical Report No. 84, pp 1-13), the cyclic profilers by Honji et al (H. Honji, A. Kaneko, and K. Kawatate (1987), xe2x80x9cSelf-governing profiling systemxe2x80x9d, Continental Shelf Research, Vol 7, No. 10, pp 1257-1265), and the Cartesian diver of Duda et al (T. F. Duda, C. S. Cox, and T. K. Deaton (1988) xe2x80x9cThe Cartesian Diver: A self-profiling Lagrangian velocity recorderxe2x80x9d, J. Atmos. Oceanic Technol, Vol 5, pp 16-33).
These early profilers were subsequently replaced by the untethered gravity driven type, which works, on the buoyancy principle for ascent or descent. Of noteworthy mention is the untethered oceanographic sensor platform developed by Hoyt and Bradley (U.S. Pat. No. 4,777,819), a torpedo shaped body which is made to free fall from a support ship. On reaching an appropriate depth, it drops an electromagnetically held ballast weight, turns around at that depth layer and then ascends under control of an interferometric homing system which guides it towards a homing beacon on a nearby vessel. On its descent the gravity profiler is negatively buoyant, and on ascent, syntactic foam cladding around the hull ensures positive buoyancy all the way up to the sea surface. The tail section of this profiler has control surfaces, which are steered by electrically operated actuators towards the recovery ship. The principal drawback of this device is that it requires special purpose deck gear on the support vessel and additional gear and homing gear equipment on a separate recovery vessel to operate effectively at sea. In addition, it would be cumbersome to operate this system in shallow coastal waters where the possibility of accidentally striking the seabed are higher than in open ocean waters.
The Autonomous Lagrangian Circulation Explorer (ALACE) is the most recent sub-surface profiler that cycles vertically from a depth where it is neutrally buoyant to the surface where it reveals its position and transmits profiled oceanographic data to the System Argos satellites. The ALACE uses buoyancy control to pump oil from an internal reservoir to an inflatable external bladder on its end-cap, thereby changing its volume, and buoyancy. Another version of the buoyancy controlled profiler is the Autonomous Oceanographic Profiler (U.S. Pat. No. 5,283,767) which has several elements in common with the ALACE system but claims the inclusion of an energy collection system which uses solar (photovoltaic) and electro-thermal (Peltier Effect) devices to charge onboard batteries. The latter system uses a moveable trim control piston to translate through a dive control cylinder which has the effect of altering the volume and hence the ballast of the profiler. The device includes Global Positioning System [GPS] capability and global bi-directional telecommunication facilities.
The profiling devices described above are based on the buoyancy principle wherein the volume of the said device is altered so as to control the buoyant force on it. A major drawback of most of these systems is that they are relatively slow compared to the present invention, and are best suited to applications in deep ocean waters. For example the ARGO floats will provide data over large spatial and temporal scales that will be used as input to global circulation models now being used to understand global climate problems. As a consequence, the number of pre-programmed descents is normally limited to 100 dives, and to maximum depth excursions of the order of 2000 dbar. The life span of these drifting profilers is typically 3 years. The ARGO or ALACE floats can be made to drift at any programmed depth before re-surfacing for a transmission burst.
The oceanographic profilers discussed above suffer from a common drawback, xe2x80x98uncontrolledxe2x80x99 variable motion through the water column. An illustration of this effect is shown in FIG. 1, which displays an actual velocity profile measured by a commercial free fall (or gravity-driven) optical profiler from a ship. A marked reduction in velocity results from a density mediated drag force is observed, when the profiler encounters a sub-surface plankton layer at about 12 m depth below the ocean surface (see * tag in FIG. 1). These effects are common in the coastal zones which display frequent stratification arising from sharp spatial gradients in ocean properties both in the horizontal ( less than 100 m) and vertical (xcx9c0.5 m) planes. The non-constant velocity in profiling systems results in a loss of valuable data records particularly near the sea surface within the first 10 meters. Data corruption of surface records is also common observed in ship based CTD profiling systems which are heaved and pitched when wind swells and waves are present, or when the winch speed is non-constant. Likewise surface optical data in free fall profilers are invariably corrupted at the start of a dive when velocity changes are abrupt, when the profiler encounters a stratified layer (see above) or when it slows down at the end of a dive (as in FIG. 1)
The present invention obviates the drawbacks experienced in most profiling system by incorporating constant velocity control in profiler motion by a user set value. This new feature will result in clean non-corrupted data records at the surface and through the entire transect of the profiler motion. This is shown to be achieved here by an on-board controller system that receives a reference input from a speed sensor on the profiler, and automatically adjusts the revolutions per minute (rpm) to a small thruster motor riding piggy-back on one end-cap of the present profiler. The output of the controller ensures constant velocity motion of the present profiler irrespective of the presence stratified ocean layers, ocean currents, wind or wave conditions that would otherwise impose external disturbances on the motion of conventional profilers, and consequent corruption in data records as is described above.
The main object of the present invention is to provide a controlled thruster-driven oceanographic profiler for coastal water which obviates the drawbacks of passive buoyancy-controlled profilers and gravity-driven profiler described above.
Another object of the present invention is to provide a means to control the thruster motor to enable the profiler to execute its motion at any specified speed through the water column.
Still another object of the present invention is to include the means to halt the motion of the profiler at any user specified depth in the water column.
Yet another object of the present invention is to provide a control system to reverse the motor thrust so as to enable the profiler to ascend to the sea surface under motor control at constant speed.